Location: Livestock Nutrient Management ResearchTitle: How does long-term crop management affect soil organic matter in the Texas High Plains?
|Baumhardt, Roland - Louis|
|ZHANG, MINCHU - University Of Alaska|
Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 7/15/2019
Publication Date: 7/29/2019
Citation: Waldrip, H., Schwartz, R.C., He, Z., Todd, R.W., Baumhardt, R.L., Parker, D.B., Zhang, M. 2019. How does long-term crop management affect soil organic matter in the Texas High Plains? [abstract]. 74th SWCS International Annual Conference, July 28-31, 2019, Pittsburg, Pennsylvania. Paper No. 14.
Technical Abstract: Soil organic carbon (SOC) is an essential component of soil fertility due to its well-known effects on water retention, microbial growth/metabolism, and nutrient mineralization. Water-extractable organic matter (WEOM), aka labile soil C, can serve as an indicator of SOC stocks and overall soil fertility. In the semi-arid southern High Plains, dryland cropping systems to produce food and forage are essential agricultural components due to limited precipitation and the declining saturated thickness of the Ogallala Aquifer for irrigation. This study examined the long-term effects of different dryland winter wheat (Triticum aestivum) cropping systems [i.e., continuous wheat (CW) and wheat-fallow rotations (WF)], tillage methods (i.e., disk plow (DP), stubble-mulch tillage (ST), and delayed stubble-mulch tillage (DST)] on the quantity and quality of soil WEOM. Ultraviolet-visible spectroscopy (UV-vis) and other analyses characterized WEOM from soils under long-term wheat systems, as compared to native rangeland. Soils were collected (0-300 mm depth) and evaluated to determine the potential sustainability of common dryland cropping systems in this semi-arid region. Results indicated that WEOM concentrations, particularly in surface soils, were rapidly depleted regardless of cropping system, compared to native rangeland, with reductions of up to 13% in 1977 and 60% in 2013. In addition, the forms of WEOM differed over time, where cropped soils from 2013 had higher concentrations of aromatic and phenolic compounds, and more lignin-like organic matter: likely due to input of wheat residue over time. In contrast, WEOM in soils from 1977 and native rangeland (2013) showed increased levels of functional groups and more humic character than cropped soils collected in 2013. This work suggested that typical conservation cropping systems may be insufficient to maintain or replenish soil WEOM after rangeland conversion to dryland cropping. However, the relatively low WEOM contents of native rangeland, along with adequate crop yields in the wheat systems over the years, brings into question the importance of this fraction of soil C to soil fertility in semi-arid regions. Ideally, conservation systems will improve WEOM/SOC stocks towards long-term sustainability, but this goal may be difficult to achieve in regions where high temperatures and limited rainfall/irrigation water tend to promote C mineralization and loss as carbon dioxide (CO2).